National Forests and the Intermountain Region 5 



Dams and great reservoirs become impossible on streams subject to 

 floods and carrying great masses of debris ; for though the construc- 

 tion may be strong enough to withstand the rush of flood waters, the 

 capacity of the reservoir is reduced with every freshet, and pres- 

 ently the reservoir is full of useless earth and rock instead of valu- 

 able water. Many small reservoirs throughout the intermountain 

 region, now useless, bear silent witness to this fact. 



There is also the item of time which might be put to productive 

 use but is wasted each year in ridding the canals of their great ac- 

 cumulation of silt and sand. In some places the disposal of these 

 accumulations has become a serious problem. On the irrigation 

 project served by the Elephant Butte storage dam in Xew Mexico, 

 enormous quantities of sand washed into the river from arroyos 

 cause difficulty and great expense in keeping the canals free of sand 

 accumulations. 



SEASONAL VARIATION IN THE VALUE OF WATEE TO CEOPS 



Less spectacular, but nevertheless real and very great, is the loss 

 in effectiveness of the water when it comes down all at once early in 

 the season and then rapidly dwindles away through the summer. 

 Studies made at the Utah Agricultural Experiment Station in regard 

 to the " duty " of water, which are showing how to make available 

 irrigation water go the farthest in the production of crops, have in- 

 dicated that nearly every crop needs late water; that is, water 

 through midsummer. Midsummer water is of much more value than 

 a superabundance at the time of the spring freshets. Irrigation 

 with early water alone frequently results in yields scarcely greater 

 than those produced in the same neighborhood by dry farming. 



Through the destruction of watershed cover early melting of the 

 snow is encouraged ; the snow drifts less, and drifts, instead of lying 

 in the shade of the trees to melt slowly as late as July, are exposed to 

 the full heat of the sun and rapidly disintegrate during the spring. 

 Also, along with the processes that destroy trees and vegetation on 

 the mountain comes the compacting of the soil, which lessens its 

 ability to absorb water. Hence surface run-off increases, spring 

 freshets are intensified, and the flow of springs, which furnishes the 

 late water in many of the streams, is decreased. Thus, although the 

 total run-off is actually increased, it is far less useful and may prove 

 dangerously destructive. 



EFFECT OF WATEE SUPPLY ON LAND VALUES 



In the intermountain region the total value of farm land amounts 

 to approximately $658,000,000. By far the greater part of this value 

 lies in the irrigated lands rather than in clry-f arm areas and pastures. 

 The water for irrigation comes almost entirely from mountains in- 

 cluded in the national forests, which cover between 29,000,000 and 

 30,000,000 acres of the intermountain region. Were the water taken 

 from the irrigated lands, their value would decrease tremendously, 

 for in some cases they would then be valuable only for grazing. Most 

 of the land now irrigated would be unprofitable as dry-farm land. It 

 would be difficult to estimate accurately the actual money value added 

 to the farm lands of the region as the result of irrigation, but it is 

 probable that the amount would reach more than half the total 

 value of the land at present, or several hundred million dollars. 



